1. Field of the Invention
This invention relates to a disengagement-preventing mechanism and, in particular, to a disengagement-preventing mechanism for a vibration isolator which is interposed between an attachment sleeve portion of prime mover and an operating rod in a bush cutter.
2. Description of Related Art
A bush cutter of this kind is generally constructed such that a cutting device equipped with a knife or blade rotor is attached at one end (a distal end portion) of an operating rod. A prime mover, such as a small air-cooled two-cycle gasoline engine, is mounted at the other end (a rear end portion) of the operating rod. The motive power from the prime mover is transmitted to the knife rotor via a transmission shaft coaxially disposed in the operating rod. A bush-cutting operation using this bush cutter can be performed by manipulation of the operating rod handled by an operator.
Assembling the operating rod and the prime mover together is performed by inserting the rear end portion of the operating rod into the attachment sleeve portion of a fan cover for the prime mover. In this way, the operating rod is detachably engaged with the attachment sleeve portion. A pipe-like retainer, equipped with a vibration isolator, is provided at the coupling between the attachment sleeve portion of the fan cover and the distal end portion of the operating rod so as to prevent the vibration of the prime mover from being transmitted to the operating rod.
FIGS. 6 and 7 illustrate one example of the structure of the coupling between the attachment sleeve portion of a fan cover of the prime mover and the rear end portion of the operating rod in a conventional bush cutter (Japanese Utility Model Publication Hei/7-10039). In FIGS. 6 and 7, a fan cover 52 covering a prime mover 51 is formed integral with an attachment sleeve portion 53 in which, or at the innermost side of which, a driving shaft 54 constituting an output power member of a centrifugal clutch (not shown) is rotatably held by a bearing 55. A tubular rubber vibration isolator 56 is fitted in the attachment sleeve portion 53 in such a manner that it contacts the inner peripheral wall of the attachment sleeve portion 53. This vibration isolator 56 is secured in a suitable way to a pipe-like retainer 57 which is coaxially disposed in contact with the inner peripheral wall of the vibration isolator 56.
A transmission shaft 59 is rotatably received within an operating rod 58. The rear end portion of the operating rod 58 is fittingly inserted into the pipe-like retainer 57 so as to be fastened by the pipe-like retainer 57. In this case, the rear end portion 59a of the transmission shaft 59 is also fittingly inserted into the driving shaft 54 supported by the bearing 55 within the fan cover 52 so that the transmission shaft 59 can be rotated in accordance with the rotation of the driving shaft 54.
As mentioned above, since the vibration isolator 56 is interposed between the attachment sleeve portion 53 of the fan cover 52 and the operating rod 58, the transmission of vibration from the prime mover 51 to the operating rod 58 can be suppressed, thereby preventing unpleasant vibration of the prime mover 51 from reaching an operator handling the operating rod 58 while carrying out bush cutting.
The pipe-like retainer 57 fixedly provided with the vibration isolator 56 is adapted to be detachable from the attachment sleeve portion 53 by inserting the pipe-like retainer 57 in the same direction as the insertion direction of the operating rod 58 to the attachment sleeve portion 53. Structural measures to prevent movement in an axial direction between the inner peripheral wall of the attachment sleeve portion 53 and the outer peripheral wall of the vibration isolator 56 during a bush cutting operation, i.e. a disengagement of the vibration isolator 56 from the attachment sleeve portion 53 during a bush cutting operation, must be taken.
Because of this, a disengagement-preventing clip 60 is disposed so as to contact the face of an external end 56a (the left side in FIG. 6) of the vibration isolator 56 so as to prevent the pipe-like retainer 57 (including the vibration isolator 56) and the operating rod 58 from being disengaged from the attachment sleeve portion 53. As shown in FIG. 7, the disengagement-preventing clip 60 is formed of a C-shaped fine steel wire having a suitable degree of elasticity and adapted to be entirely received in the opening section of the attachment sleeve portion 53. This disengagement-preventing clip 60 is provided with a couple of angled portions 60a diametrically facing one another. The angled portions 60a are adapted to be elastically fitted in a couple of slits 61 which are formed along the periphery of the attachment sleeve portion 53 and spaced apart by an angle of 180 degrees so as to diametrically face each other. Fitting the angled portions 60a in these slits 61 permits the disengagement-preventing clip 60 to be locked within the attachment sleeve portion 53. At the same time, the external end face 56a of the vibration isolator 56 is brought into contact with the disengagement-preventing clip 60 thereby preventing the vibration isolator 56 from being disengaged from the attachment sleeve portion 53.
The disengagement-preventing clip 60 is designed to be set in the attachment sleeve portion 53 in such a manner that the clip 60 is entirely disposed within the attachment sleeve portion 53 and the elastic fitting thereof in the aforementioned couple of slits 61 is effected by directing the clip 60 from the inside to the outside of the attachment sleeve portion 53. Consequently, the clip 60 must be introduced into the attachment sleeve portion 53 by directing it in the same direction as the direction in which the pipe-like retainer 57 carrying the vibration isolator 56 is inserted into the attachment sleeve portion 53. In this case, the outer diameter of the clip 60 must be contracted against the elastic force of the clip 60 so as to allow the clip 60 to be introduced from the open end portion of the attachment sleeve portion 53 into the interior of the attachment sleeve portion 53. Both the operation of setting the clip 60 in the attachment sleeve portion 53 and the operation of detaching the clip 60 from the attachment sleeve portion 53 are very troublesome.